After turning a taper by the tailstock setover
produced by the same amount of setover of the
tailstock, because for one taper the length of the work
method, do not forget to realign the centers for
between centers is greater than for the other. THE
straight turning of your next job.
CLOSER THE DEAD CENTER IS To THE LIVE
USING the COMPOUND REST. --The
CENTER, THE STEEPER WILL BE THE TAPER
compound rest is generally used for short, steep
PRODUCED. Suppose you want to turn a taper on
tapers. Set it at the angle the taper will make with the
the full length of a piece 12 inches long with one end
center line (that is, half of the included angle of the
having a diameter of 3 inches, and the other end a
taper. Then, feed the tool to the work at this angle by
diameter of 2 inches. The small end is to be 1 inch
using the compound rest feed screw. The length of
smaller than the large end; so you set the tailstock
taper you can machine is short because the travel of
over one-half of this amount or 1/2 inch in this
the compound rest is limited.
example. Thus, at one end the cutting tool will be
One example of using the compound rest for taper
1/2 inch closer to the center of the work than at the
work is the truing of a lathe center. Other examples
other end; so the diameter of the finished job will be
2 1/2 or 1 inch less at the small end. Since the
are refacing an angle type valve disk and machining
the face of a bevel gear. Such jobs are often referred
piece is 12 inches long, you have produced a taper of
to as working to an angle rather than as taper work.
1 inch per foot. Now, if you wish to produce a taper
of 1 inch per foot on a piece only 6 inches long, the
The graduations marked on the compound rest
small end will be only 1/2 inch less in diameter than
provide a quick means for setting it to the angle
the larger end, so you should set over the tailstock
desired. When the compound rest is set at zero, the
1/4 inch or one-half of the distance used for the
cutting tool is perpendicular to the lathe axis. When
12-inch length.
the compound rest is set at 90 on either side of zero,
the cutting tool is parallel to the lathe axis.
By now you can see that the setover is
proportional to the length between centers. Setover is
To set up the compound rest for taper turning, first
computed by using the following formula:
determine the angle to be cut, measured from the
center line. This angle is half of the included angle of
the taper you plan to cut. Then, set the compound rest
to the complement of the angle to be cut (90 minus
the angle to be cut). For example, to machine a 50
where:
included angle (25 angle with the center line), set the
compound rest at 9025, or 65.
S = setover in inches
When you must set the compound rest very
accurately, to a fraction of a degree for example, run
T = taper per foot in inches
the carriage up to the faceplate and set the compound
rest with a vernier bevel protractor set to the required
angle. Hold the blade of the protractor on the flat
L = length of taper in inches
surface of the faceplate and hold the base of the
protractor against the finished side of the compound
L
= length in feet of taper
rest.
12
USING THE TAPER ATTACHMENT.--For
Remember that L is the length of the work from
turning and boring long tapers with accuracy, the
the live center to the dead or ball bearing center. If the
taper attachment is indispensable. It is especially
work is on a mandrel, L is the length of the mandrel
useful in duplicating work; you can turn and bore
between centers. You cannot use the setover tailstock
identical tapers with one setting of the taper guide bar.
method for steep tapers because 2the setover would
Set the guide bar at an angle to the lathe that
be too great and the work would not be properly
corresponds to the desired taper. The tool cross slide
supported by the lathe centers. The bearing surface
will be moved laterally by a shoe, which slides on the
becomes less and less satisfactory as the setover is
guide bar as the carriage moves longitudinally. The
cutting tool will move along a line parallel to the
increased. Do not exceed 0.250-inch setover since
guide bar. The taper produced will have the same
your center hole and your tailstock center will not
angular measurement as that set on the guide bar. The
align properly.
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